Currently, ultrasonic range finders are widely used in many fields such as in engineering. Usually, the ultrasonic range finders detect an ultrasonic propagation time within a measured distance, and then the measured distance can be obtained by multiplying the ultrasonic propagation time by an ultrasonic propagation speed. But the ultrasonic propagation speed is not a constant value and often varies with respect to changes in the environment. Environmental factors affecting the ultrasonic propagation speed include the temperature, humidity, atmospheric air pressure and other atmosphere components. However, the temperature and the humidity are the leading factors.
China patent No. ZL 02248586.4 discloses an ultrasonic range finder with a temperature compensation circuit in which a temperature-sensitive resistor of the temperature compensation circuit senses the environment temperature so that the ultrasonic propagation speed can be compensated. However, it does not compensate for other environment factors and so the measuring precision can not be ensured. U.S. Pat. No. 4,581,726 discloses an ultrasonic range finder with a sensor detecting multiple atmospheric characteristics. However, such a sensor is very expensive causing the manufacturing cost of the range finder to also be very expensive.
Additionally, when the above-mentioned range finder is moved from one environment to another environment, the above-mentioned sensor will measure the atmospheric characteristics precisely only after a long time (maybe several minutes depending on the conditions) causing the results in the measuring time to be lengthened. It is obvious that this limits the use of the disclosed ultrasonic range finder.
The present invention is provided to solve these and other problems.